Benzobisthiazole-based Regioisomeric Donor-Acceptor Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

Abstract

This study develops an effective molecular isomerization strategy to enhance photocatalytic hydrogen peroxide (H2O2) production by leveraging the structural tunability of benzobisthiazole (BT)—an electron-deficient planar heterocycle with superior optoelectronic properties and chemical stability. Unlike conventional isomeric covalent organic frameworks (COFs) which focus on symmetric or unidirectional conjugation systems, we exploit the two orthogonal π-conjugation pathways (2,6- versus 4,8-substitution) of BT to construct regioisomeric COFs with distinct topological connectivity, a design that remains rarely explored for photocatalytic H2O2 generation. Utilizing subsitution-position flexibility of BT, two regioisomeric monomers, namely 2,6-BT-CHO and 4,8-BT-CHOpro, were designed and polymerized into highly crystalline donor-acceptor (D-A) covalent organic frameworks (COFs): 2,6-BT-COF and 4,8-BT-COF. These COFs exhibit high surface areas, extended π-conjugation, and excellent light-harvesting capabilities, rendering them ideal photocatalysts. Remarkably, under visible-light irradiation in pure water, 2,6-BT-COF achieved a H2O2 production rate of 1638 µmol·g−1·h−1, outperforming 4,8-BT-COF (1046 µmol·g−1·h−1) by about 57%. Structural and photophysical analyses reveal that this pronounced performance difference stems from the critical influence of molecular topology on charge separation, exciton dissociation, and redox kinetics. Specifically, 2,6-BT-COF facilitates more efficient intramolecular charge transfer and suppresses charge recombination losses compared its 4,8-substituted counterpart. This work not only presents two novel, structurally well-defined COF photocatalysts but also establishes a design principle for optimizing photocatalytic efficiency through precise control of molecular connectivity. (Figure presented.)